Patent GB-1135814-A (GB)
Title: Collapsible mast assembly for a fork lift truck
IPC: B66F9/20
Filed: 1966-09-27
Abstract: 1,135,814. Masted lift trucks; hydraulic jacks. STEINBOCK, G.m.b.H. 27 Sept., 1966 [6 May, 1966; 20 June, 1966], No. 43156/66. Headings B8H and B8J. A fork lift truck mast assembly comprises a fixed lower mast part 1, Fig. 4, a movable upper mast part 2, a fork member movably mounted on the part 2, and a telescopic ram and chains or cables 11, 12 for moving the part 2 and the fork member, the height of the ram when in its fully retracted position being approximately half the height of the mast when the latter is also fully retracted. The ram has a main cylinder 3, an open-bottomed pistoncylinder 4 telescopically movable within the cylinder 3, and a piston 6 movably mounted within the piston-cylinder 4 and connected to a piston rod 5. The mast may have more than two parts. Chains or cables 11 extend from an anchorage 16 on the part 2 round pulleys 8 on the piston rod 5 and pulleys 10 on the part 2 to an anchorage 15 on the fork member, and chains or cables 12 extend from an anchorage 13 on the part 1 round pulleys 9 on the piston-cylinder 4 to an anchorage 14 on the part 2. Hydraulic fluid enters and leaves the cylinder 3 through a connection 19 via a tube 23 and enters and leaves the pistoncylinder 4 through a connection 18 via a flexible tube 20, coiled on a spring-loaded drum 21, and a tube 22. Alternatively, the tube 20 may be spring-suspended and the drum 21 omitted. A control valve 24 connects the tubes 22, 23 to a supply pipe 34 leading from a tank 32 through a pump 33, and a return pipe 31 leading back to the tank 32. The valve body has recesses 26, 27 for selectively connecting the tubes 22, 23 to the pipes 31, 34 when the valve body is rotated by a lever 25. In operation fluid is supplied to the piston-cylinder 4 to move the piston 6 down and lift the fork member, the movement of which is limited by a limit switch and a pressure release valve, Fig. 7 (not shown). The tubes 22, 23 are then both connected to the supply pipe 34, Fig. 6 (not shown), and consequently the piston-cylinder 4 is connected to the cylinder 3 with fluid flowing from the former to the latter; this flow is throttled by the valve 24 so that the piston 6 is prevented from rising in the piston-cylinder 4 faster than the latter in the cylinder 3. In a second embodiment, Figs. 8 to 11 (not shown), the bottom end of the piston-cylinder 4 is closed and the piston 6 is replaced by the end of the piston rod 5. The fluid may enter and leave the piston-cylinder 4 through the rod 5. The chains or cables 11 extend from an anchorage at the top of the piston-cylinder 4 round pulleys 8 carried by the piston rod 5, pulleys (35) at the top of the pistoncylinder 4 and the pulleys 10 on the part 2 to the anchorage 15 on the fork member. In a third embodiment, Figs. 12 to 14 (not shown), the piston 6 and the piston rod 5 are omitted. The chains or cables 11 extend from the anchorage 16 which in this embodiment is disposed intermediate the ends of the part 2 round pulleys 8, mounted at the top of the pistoncylinder 4, and the pulleys 10 on the part 2 to the anchorage 15 on the fork member.